1. Field of the Invention
The present invention relates to an image scanner that is used for scanning documents of a digital copying machine and an input terminal of a personal computer, and a peak detecting processing method of an image scanner.
2. Description of the Related Art
As a scanner that is used in digital copying machines and/or personal computers for scanning optical image data from documents using a Charge Coupled Device (hereinafter, abbreviated as CCD) for scanning optical image data from documents, an apparatus is so far disclosed in Japanese Patent Application No. 8-251355. This scanner scans optical image data and discriminates whether the data are color images or monochromatic images at the time of pre-scanning using color CCD sensors or a monochromatic CCD sensor having a rotary color separation filter and increases a scanning speed for a monochromic image and expands a scanning region. Further, an apparatus having color CCD sensors and a monochromatic CCD sensor arranged side by side is so far disclosed in Japanese Patent Application No. 2001-238053. This apparatus simultaneously scans image data by color CCD sensors and a monochromatic CCD sensor and eliminates noise components by comparing color output signals and monochromatic output signals.
However, the above-mentioned conventional image scanners are not intended to save circuits for processing output signals from sensors and achieve a low cost of an image scanner in an image scanner equipped with color CCD sensors and a monochromatic CCD sensor.
On the other hand, in a four-line CCD sensor equipped with color CCD sensors and a monochromatic CCD sensor, in order to reduce a cost, a scanner is developed to use the same output signal processor commonly by switching color CCD sensors and a monochromatic CCD sensor by a switch. However, this scanner using the output signal processor commonly always sets a gain for amplifiers of the output signal processors by detecting the peak value of sensitivity of the color CCD sensors in spite of the color CCD sensors and the monochromatic CCD sensor equipped.
That is, in this image scanner commonly using the output signal processor, the amplifiers of the output signal processor are amplified according to the sensitivity of the color CCD sensors even when scanning monochromatic images by the monochromatic CCD sensor and signals scanned by the monochromatic CCD sensor are processed. Therefore, such defects are actually generated in the monochromatic image scanning performance as, for example, a gain of the amplifier and sensitivity of the monochromatic CCD sensor become different, color shading is produced on scanned images, dark areas of the images tend to lose detail and white wash out, etc.
Accordingly, in an image scanner using a four-line CCD sensor provided with color and monochromatic CCD sensors, it is demanded to realize a high grade image scanning of both color and monochromatic images without impairing the achievement of a low cost by setting gains of amplifiers faithfully to the respective color and monochromatic CCD sensors.